Composite membranes and methods for making same

Abstract

Composite membranes that are adapted for separation, purification, filtration, analysis, reaction and sensing. The composite membranes can include a porous support structure having elongate pore channels extending through the support structure. The composite membrane also includes an active layer comprising an active layer material, where the active layer material is completely disposed within the pore channels between the surfaces of the support structure. The active layer is intimately integrated within the support structure, thus enabling great robustness, reliability, resistance to mechanical stress and thermal cycling, and high selectivity. Methods for the fabrication of composite membranes are also provided.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority to U.S. Provisional Patent Application Ser. No. 60 / 767513, filed on May 7, 2006, which is incorporated herein by reference in its entirety.STATEMENT REGARDING FEDERALLY-FUNDED RESEARCH [0002] This invention was funded by the National Science Foundation under Grant No. DMI-0420147 (Phase I) and Grant No. OII-0548757 (Phase II), and by the Department of Energy under Grant No. DE-FG02-04ER84086, both administered by the Small Business Innovation Research (SBIR) program. The Government has certain rights in this invention.BACKGROUND OF THE INVENTION [0003] 1. Field of the Invention [0004] The present invention relates to composite membranes, methods for making composite membranes and applications of the composite membranes. The composite membranes include a porous support structure and one or more active layers disposed within the pores of the support structure. [0005] 2. Description of Related Art [0006] Ef...

AI Technical Summary

Benefits of technology

[0022] The use of anodic aluminum oxide can enable the active layer to have a thickness in the range of from below about 1 nm to tens of micrometers.

[0023] For composite membranes useful for H2 separation, the thickness of the active layer of metal or metal alloy can be as thin as 10 nm, enabling an increase in H2 flux by orders of magnitude as compared to conventional foil membranes or thin film supported membranes, while maintaining high permselectivity for H2.

[0024] According to one aspect of the present invention, the small size of the nanostructures of active layer materials embedded within the pores also greatly increases their resistance to thermal cycling and / or mechanical loads, reducing defect formation. Nanostructured materials in general have greater mechanical strength and greater integrity during thermal cycling as compared to microstructured composite membranes.

[0025] According to one aspect of the present invention, the location of the active layer within the pores of the support structure can be controlled such that the active layer is disposed at a predetermined position beneath the surface of the support structure. This can be achieved, for example, through the use of sacrificial layer(s) during manufacture of the composite membrane. Placement of the active layer within the thickness of the support structure, as compared to placement on the membrane surface, enables a composite membrane having increased performance and increased reliability. Advantages can include increased adhesion of the active layer to the support structure, and increased resistance to thermal cycling and mechanical abrasion damage.

[0026] According to one aspect of the present invention, the active layer is comprised of several different materials disposed in multiple layers that can be deposited either consecutively or concurrently. The material layers can be oriented either perpendicular or parallel to the pore axis to achieve desired separation performance.

Problems solved by technology

Although Pd-based bulk foils exhibit near-infinite selectivity for H2, they are expensive and have poor flux due to the required foil thickness.

However, the fabrication of thin-film Pd supported membranes that have the required defect-free structure requires a Pd thickness of at least 10 μm to 50 μm, which is too thick for many applications, such as H2 separation in portable fuel cell reformers.

Furthermore, the reliability of supported membranes is limited by the poor mechanical integrity of the thin metal layers deposited onto the porous support.

Further, the poor mechanical integrity is often exacerbated by temperature cycling and / or mechanical loads that are encountered in use.

Also, the reliable sealing of thin supported membranes is also challenging and the cost of the manufacturing and integration of such membranes has hindered their widespread application.

However, the total area of the supported Pd membrane was small, limiting the total flux.

Additionally, the Pd windows ruptured when subjected to transmembrane pressures of about 0.5 bar, and the thermal reliability of the thin Pd film on Si was a problem due to the mismatch of temperature expansion coefficients.

Although thin-film supported membranes, such those described above for H2 separation, have been fabricated, their commercial utility has not been realized.

Such membranes have problems related to poor adhesion of the Pd layer to the support, damage to the Pd layer caused by thermal cycling and susceptibility to damage from mechanical abrasion

However, although these membranes could provide much thinner active layer, the active layer is still on the membrane surface and is prone to hydrogen embrittlement and mechanical damage.

The method does not allow the formation of the active layer disposed entirely within the nanoporous support structure.

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